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Aspect Ratio Calculator — 16:9, 4:3, 1:1 & Custom

Resize an image or video while keeping the aspect ratio. Type either width or height — the other fills automatically.

Original

Aspect ratio: 16:9

New size (preserves ratio)

Type either dimension — the other fills automatically.

16:9

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About this tool

Calculate any aspect ratio — 16:9, 4:3, 1:1, 21:9 and custom

Enter a width or a height and lock a ratio — the other dimension fills in automatically, so you get exact pixel sizes without doing the math by hand. Works for the common presets (16:9 widescreen, 4:3, 1:1 square, 9:16 vertical, 21:9 ultrawide, 3:2 photo) or any custom ratio you type.

Common 16:9 resolutions

  • 1920 × 1080 — 1080p Full HD
  • 1280 × 720 — 720p HD
  • 2560 × 1440 — 1440p QHD
  • 3840 × 2160 — 4K UHD

How to calculate an aspect ratio

Divide width by height and simplify: 1920 ÷ 1080 = 1.777…, which is 16:9. To resize while keeping the ratio, multiply both sides by the same factor — halving 1920 × 1080 gives 960 × 540, still 16:9. This calculator does that instantly so images and video never end up stretched or squished.

Resize or crop a photo to a ratio

Use it to find the target pixel size before cropping a picture to 1:1 for an Instagram post, 16:9 for a YouTube thumbnail, or 9:16 for Reels and Stories. Everything runs in your browser — nothing is uploaded.

How to use the Aspect Ratio Calculator

Takes about a minute. No signup, no download, your data stays in your browser.

  1. 1
    Open the tool. Scroll up to the Aspect Ratio Calculator above — it loads instantly in your browser, no install needed.
  2. 2
    Enter your values. The fields come pre-filled with realistic defaults so you can see how it works — replace them with your own numbers.
  3. 3
    Read the result. The output updates instantly. Copy or share it — nothing is uploaded to a server, everything stays on your device.

Frequently asked questions

Common questions about the Aspect Ratio Calculator.

What is an aspect ratio?

An aspect ratio is the proportional relationship between width and height, written as width:height — for example 16:9 means 16 units wide for every 9 tall.

How do I resize an image while keeping the aspect ratio?

Type either the new width or the new height and the other value fills in automatically, so the image or video keeps its proportions and never looks stretched.

What are the most common aspect ratios?

16:9 (HD video, YouTube, most screens), 4:3 (older monitors and cameras), 1:1 (square, Instagram posts), 9:16 (vertical — Stories, Reels, TikTok), and 21:9 (ultrawide cinema).

What resolutions are 16:9?

Common 16:9 resolutions are 1280×720 (720p), 1920×1080 (1080p), 2560×1440 (1440p) and 3840×2160 (4K).

How do I work out the aspect ratio from pixel dimensions?

Divide the width by the height and simplify the fraction. For example 1920×1080 divides down to 16:9, and 1080×1080 is 1:1.

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